If it's interesting and not salaciously voyeuristic, I grab my camera.
Here's some of what's been visible --- nothing profound; just for fun:
Hawk drying its wings in the sun after a rainy night:
Many schools, including the Massachusetts College of Art and Design and the New England School of Photography, are nearby, and some student projects appear on the roofs on a regular basis:
Ordinary things also happen:
The rest of the album: